U.S. Pat. No. 2,973,380, Swern, issued Feb. 28, 1961, discloses alpha-phosphono acid ester plasticizer compounds. In the form of partially hydrolyzed alpha-dialkylphosphono carboxylic acids, the compounds are said to be useful in making lubricant greases.
U.S. Pat. No. 2,185,541, Cahn, issued Jan. 2, 1940, describes a wide variety of alpha-substituted carboxylic acids as interface modifying agents. The hydrophilic group at the alpha position generally is an oxygenated sulfur or phosphorus group, and can be phosphonic acid. The patent also states that the carboxyl group of the acid can be esterified or converted to an amide.
U.S. Pat. No. 2,363,510, Farrington et al., issued Nov. 28, 1944, discloses alpha-, beta- and gamma-substituted carboxylate salts as non-corrosive detergent additives for lubricants. The substituents must contain either nitrogen, phosphorus, arsenic, antimony or bismuth, and can be phospho and phosphonato groups.
U.S. Pat. No. 3,830,885, Petersen, issued Aug. 20, 1974, discloses certain dialkyl carbamylphosphonates useful as intermediates in the preparation of dialkyl N,N-dialkoxymethyl carbamylphosphonate flameproofing additives.
German Pat. No. 27 56 488, Schmidt et al., published June 29, 1978, discloses dithiophosphato acid and amide compounds which are said to be useful as non-corrosive extreme pressure additives for lubricants.
Zinc dialkyl dithiophosphates are commonly used in lubricants as antiwear additives and antioxidants. However, since these compounds do not reduce friction between moving surfaces, and can even increase friction under certain conditions, lubricants containing them often also require special additives to minimize energy losses due to friction. In order to reduce friction and thereby improve fuel efficiency, crankcase lubricants have recently been prepared using low-viscosity base oils. However, current antiwear additives do not provide adequate wear protection in such low-viscosity oils. New antiwear additives which provide lower phosphorus levels than the zinc dialkyl dithiophosphates are also needed for crankcase lubricants in order to reduce phosphorus poisoning of catalytic converters and other emission control equipment. Finally, more effective additives for liquid hydrocarbon fuels are needed to reduce wear and friction in fuel pumps and the upper cylinders of internal combustion engines.
While some alpha-phosphono carboxylic acids and esters known in the art could provide antiwear and friction-reducing benefits in lubricants and fuels, it has been found that they are generally too corrosive to be used in such compositions. Thus, there is a continuing need for the development of improved antiwear and friction-reducing additives for lubricants and fuels.